cal·trop (kăltrəp, kôl-)
1. See water chestnut.
2. Any of various plants bearing small spiny fruits, especially of the genera Tribulus and Kallstroemia.
3. A metal device with four projecting spikes so arranged that when three of the spikes are on the ground, the fourth points upward, used as a hazard to pneumatic tires or to the hooves of horses.
[Middle English calketrappe, from Norman French and from Old English calcatrippe, thistle, both from Medieval Latin calcatrippa, thistle : possibly from Latin calcāre, to tread on; see CALQUE + trappa, trap (of Germanic origin).]
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